Currently, the use of ctDNA detection in cancer therapy has been approved by the US Food and Drug Administration as a treatment determinant (osimertinib or erlotinib) in non-small-cell lung carcinoma (NSCLC) patients with an EGFR mutation in the event that a tumor biopsy cannot be performed (US Food & Drug Administration, 2016). The gene discussed is EGFR; the disease is non-small cell lung carcinoma.